Top 3-5 cost efficient ways to decrease body roll? - Page 9 - PeachParts Mercedes-Benz Forum

leathermang · #**121** 01-16-2011, 12:05 AM

Quote:

Originally Posted by moon161

LM:
Simple experiments have been a tool of important skeptics, from Thomas onward.
Try this:
3 identical bungee cords 1 foot or so long, an appropriate weight, tape measure, hook to hang things from or maybe the top of a door. While not useful as a compression spring, bungee cords work as an extension spring, and should convey the point.
1.
a. Hang 1 cord, put enough weight on it to stretch it in the most linear range, say by 25-50%. Maybe a gallon or 2 of milk or water. Note the extension (change in length) and force (the weight of what you hung on it, 8lb/gallon for water).
b. The spring constant K1 is the ratio of force/extension.

2.
a.Add a second cord, so it hangs from the first, and hang the weight from the second. You should have Ceiling, cord 1, cord 2, weight.
b. Note that if you lift the first cord off the hook or lift the second cord so that it lifts off the hook of the first, the weight is the same, if you neglect the small weight of the bungee cords.
c. Record the extension of the endpoints of the first and second bungee cords. Do they both increase by the same length? Compare to 1a.
d. Note the extension of the combination of both cords, or how much the lower end or cord 2 moves.
e. The spring constant of the combination = weight/total extension. Theory says that 1/k = 1/k1 + 1/k2

3. Add a third, repeat as above.

Were you drinking when you posted this post ? We are talking springs in compression and you change to bungee cords IN ELONGATION !!!!

#**122** 01-16-2011, 12:53 AM

I found a decent explanation here:

http://www.physicsforums.com/showthread.php?t=205524

moon161 · #**123** 01-16-2011, 01:08 AM

Please use imagination as required, or substitute springs in compression. I'm done.

winmutt · #**124** 01-16-2011, 01:23 AM

Quote:

Originally Posted by leathermang

I totally agree. If a person would read all the FSM CHASSIS Manuals for these cars... there are two of them for the 123's... they would appreciate better how much effort went into making these cars ride the way they do.... and last doing it... It also has the chart for the number of wire sizes MB made available for these cars ... including stiffer ones for ' bad road countries'... a simple PROPER way to increase ride stiffness and lessen role which could be matched to other heavy duty gear made designed to work together....

What makes it "proper"? There is always room for improvement in everything, everyday.

I am always amazed how people make suspension out to be rocket science. Even rocket science in its rudimentary form is pretty basic. And the suspension setup in the w123 is pretty basic. It was not handed down from god to MB so that various configurations tested for every possible pothole in the west sahara. I will certainly agree that they tested most potholes in the west sahara, most switch backs in the alps and plenty of laps on the ring; but this is not the end all.

A simple example, the rear of my w123 is dropped significantly enough that my camber is greater than that of any MB config in the FSM. The downside? Wet cornering acceleration. Their practically is none. So I just know to take it easy on the right pedal. The upside? Weekend drives in the north georgia mountains?

Does everyone in the US take weekend trips in the north georgia mountains? Particularly the 19 60 180 Loop? No. Did MB? No. Could my current setup be improved upon? Of course. Did MB offer any combination of springs and shocks comparable to mine? Unlikely.

However, what it comes down to is that I love the way it handles. I have LEARNED to love it. Learned its shortcomings and its merits.

I often wonder if that last look on my grandfathers face as he drove his 190SL off the cliff in the alps was one of terror or glee. From what I have heard about him and his driving habits and how much he loved that car, I can only think it was one big effing smile.

leathermang · #**125** 01-16-2011, 01:24 AM

Quote:

Originally Posted by moon161

I'm done.

I doubt that. Unless you realized your mistake and don't want to admit it. I have never seen anyone head so far into the hinterlands to avoid using the actual objects under discussion. Sewer pipes, bungie cords,springs in elongation..... did I miss any ?

#**126** 01-16-2011, 01:36 AM

Quote:

Originally Posted by leathermang

I doubt that. Unless you realized your mistake and don't want to admit it. I have never seen anyone head so far into the hinterlands to avoid using the actual objects under discussion. Sewer pipes, bungie cords,springs in elongation..... did I miss any ?

He's actually correct, read the link I posted above.

leathermang · #**127** 01-16-2011, 01:38 AM

Quote:

Originally Posted by winmutt

What makes it "proper"? There is always room for improvement in everything, everyday.

That may be true... but that is not to say that just anybody walking around is able to improve any given item.
Proper means that you don't wear out the tires unnecessarily fast and that you are able to keep the car under control with regards to safety.

To look at a MB suspension and think " I can improve that with no serious downsides " may be a little to simple minded.

There is the story about John Delorean ... when he was a big wig at General Motors.... but still driving a Mercedes... driving the car into the research department and asking them why their GM products could not drive and handle like his MB...

The result was the suspension on the Monte Carlo.... and my aunt owned one of those... it was a totally different feel than most cars...

I am just saying that if someone does not really understand all the functions of the MB suspension and how they work together... then their chances of messing up something are great.

Check out the FSM pictures on ' normal tire wear patterns'.... they are even different from what you see on other cars...

t walgamuth · #**128** 01-16-2011, 08:57 AM

Quote:

Originally Posted by Craig

He's actually correct, read the link I posted above.

He is correct. Using the bungies is an excellent way to illustrate the problem. any scientific principle should be easy to illustrate with simple devices. One has to have an open mind to understand, though.

t walgamuth · #**129** 01-16-2011, 09:31 AM

The illustration of the two springs sitting side by side vs end to end is illustrative. I did not follow all the formulae but I am pretty sure I know the answer to the question:
1. If side by side the compresive rate is doubled. IE 100# applied with the spings this way compresses the springs half as much as with one spring.
2. sitting one spring on top of the other with no connection of the ends of the coil will equal the same rate of compression as a single spring, right?

Now I will add a third example:
Weld two springs end to end connecting the coils so that you have one continuous coil. This example creates a spring with much less resistence per a given weight. The reason is that the longer coil has more leverage on the torsional resistance of the section of the spring.

You have to be careful how you look at things, particularly in design of building sturctures since if there is a failure people can die.

Remember the collapse of the walkways in the Regency Hiatt about 30 years ago? The reason for the collapse was so simple it can hardly be imagined but also was easily overlooked. People did die too.

The walkways were stacked on top of one another, lets just say there were six going across an atrium space all perfectly aligned above one another. They were too long for a simple span so there were steel tension rods added to support lets say in two locations in the length of the walkway (bridge). The Engineer who designed the walkways specifiec one drawbar which was attached to a big beam above it all and going down through the walkways with a big nut under each walkway to support the load of the walkways. Picture one large rod 80 feet long with a threaded portion and a nut every twelve feet which supported a walkway at each floor level.

The rod is sized so that it will carry all of the loads of the six bridge walkways. The nuts each carry the weight of one walkway.

During construction the contractor comes along and says (as they always do) "This is silly, how can you get an 80 foot rod with threads every twelve feet made and into the space, let alone how to get it installed in all those walkways". I will just use rods the length of one floor level and use a connector (like a long nut which you can insert the threaded rod into each end of) between the rods of the same diameter as the nuts specified.

So that was done. The problem is that the connector was the same size and strength as the nuts. This means they were designed only to carry the load of one floor level of the walkways, and the load of the rod is now passing through the connectors. The bottom walkway is not a problem but the top walkway connector is now carrying the load of all six platform walkways.

Now as long as there was not too many people using the walkways they were fine, but on (lets say) new years eve the place was filled and the people lined up the walkways looking down on the festivities in the atrium and the walkways begain to approach their total design load (they have to be designed to carry a load of people standing in a mass belly to back and shoulder to shoulder since that is possible to have, no matter how unlikely).

And so the connectors failed. And the bridges came raining down from the top of the Regency Hiatt, and people died.

The lesson learned is two fold (from my point of view as a designer of buildings including structures):
1. Be careful of what you design, the men in the field will have to actually build it, so be sure it can be built.

because

2. If they cannot build it the way you have carefully designed it they will build it another way which suits their working conditions. It may look like what you designed but it will not BE what you designed.

I think there is a coorelationship of the bridge/rods/nuts story to the springs. I won't try to explain it in a direct way though. For me I think knowing about the one helped me figure out the other.

t walgamuth · #**130** 01-16-2011, 09:43 AM

I just wikipediaed the collapse of the Kansas City Regency Hiatt. I did not have all the details exactly right but the principle is correct. 114 people died and 200 were injured. Worst building collapse disaster in US history.

All the structural Engineers who approved the change lost their licenses and the firm lost its license to practice and 140 million in damages were paid out.

(nowadays that much might be paid to one victim!)

It was 1981.

winmutt · #**131** 01-16-2011, 10:00 AM

Quote:

Originally Posted by leathermang

Proper means that you don't wear out the tires unnecessarily fast and that you are able to keep the car under control with regards to safety.

Whats more important, control, safety or tire wear?

whunter · #**132** 01-16-2011, 11:07 AM

Quote:

Originally Posted by English Bulldog

i am open to real life experience in this type of cut commentary.

Anybody who cut springs like in the two tone picture like to comment on how the ride is?

Anybody who didn't ever cut w123 springs like in the picture like to comment but please declare it is educated speculation and opinion.

More credibility to those with bilstein heavy duty and cut springs is fair right.

(If anybody comments, then they didn't die of kidney failure.

)

Where did you get death from???

I have done what you contemplate many times through the years, by customer demand.

The cars are acutely painful for me to ride in, (previous spinal injury and kidney stones several times per year).

whunter · #**133** 01-16-2011, 11:15 AM

Quote:

Originally Posted by winmutt

This sounds more like a legal disclaimer. I fail to see how adjusting the starting point in the normal geometery can exceed engineered stress limits etc etc etc.

Taking the NORMAL geometery, chop it by 1/3 or more = it is no longer normal.

winmutt · #**134** 01-16-2011, 11:19 AM

Quote:

Originally Posted by whunter

Taking the NORMAL geometery, chop it by 1/3 or more = it is no longer normal.

Yes but its still in the realms of the normal travel. The thing I dont get is that my ride height could easily be obtained in a stock 123 simply by loading up the trunk with luggage and 4 ppl in the car. Anything abnormal about that? I can garuntee you that the MB testers certainly did the same on the autobahn at speed for many hours.